Field of the Invention
This invention relates to a light deflecting apparatus using a rotary polygon mirror, and more particularly, to a light deflecting apparatus using a rotary polygon mirror utilizing a pneumatic bearing.
Description of the Related Art
Heretofore, a light deflecting apparatus using a rotary polygon mirror for reflecting and scanning a light beam in a specified direction by using a rotary polygon mirror (hereinafter, referred to as "polygon mirror"), which has a construction shown in FIG. 1, has been proposed.
That is, in FIG. 1, 1 generally shows the light deflecting apparatus using a rotary polygon mirror. The light deflecting apparatus is composed of a lower block 2, middle block 6, upper block 3, pipe block 4 which is provided between the lower block 2 and the middle block 6, and pipe block 5 which is provided between the middle block 6 and the upper block 3.
At the inner circumference of the middle block 6, an iron core 21 wounded by a magnet wire 28 is provided, and at the inner circumferential surface of the iron core 21, a stator ring 22 made of, for example, ceramic is fixed thereto.
Further, at the inner circumferential surface of the stator ring 22, a rotor ring 23 made of resinous material etc., is engaged freely, being separated by a slight space 25, and at the inner circumferential surface of the rotor ring 23, a shaft 26, which at its circumference a magnet 24 is affixed by engaging, is engaged. Therefore, a rotor unit constituted by the shaft 26, magnet 24, and rotor ring 23 is supported freely in revolution with respect to the inner circumferential surface of the stator ring 22, being separated by the slight space 25.
At the upper end of the shaft 26, a thrust bearing member 37 is fixed with screws 36A and 36B. The thrust bearing member 37 is arranged facing a disc member 31, which is fixed to the pipe block 5, across a slight space.
The thrust bearing member 37 is engaged with a polygon mirror 33 of which its circumferential side is formed by a plurality of mirrors 33A, and held to the shaft 26 with a screw 34 through a fixed disc 35.
On the other hand, at the lower end of the shaft 26, a thrust bearing member 42 is fixed with screws 46A and 46B, and the thrust bearing member 42 is arranged facing a disc member 41 fixed to the pipe block 4 across a slight space.
At the thrust bearing member 42, a disc member 43 weighing as much as the polygon mirror 33 is engaged, and held to the shaft 26 with a screw 44 through a fixed disc 45. Accordingly, the balance is kept by the disc member 43 and the polygon mirror 33, so that the smooth revolution of the shaft 26 can be realized.
In the middle block 6, a path 6A for introducing compressed air is formed, and the compressed air taken from a joint 15 is introduced into a path 21A formed at the iron core 21. Further, the compressed air introduced into the path 21A is supplied to the space 25 formed between the stator ring 22 and the rotor ring 23 through a choke tube formed in the stator ring 22.
In such a manner, compressed air is introduced into the space 25, so that the shaft 26 is supported via a pneumatic layer in the radial direction. The compressed air introduced into the space 25 is exhausted from joints 11 and 13 through paths 4B and 5B formed in the pipe blocks 4 and 5 respectively.
On the other hand, a path 4A for introducing compressed air is formed in the pipe block 4, so that the compressed air taken from a joint 12 is supplied to a space formed between the disc member 41 and the thrust bearing member 42 through the path 4A. By introducing compressed air into the space, the thrust bearing member 42 and the shaft 26 fixed thereto are supported in the thrust direction via the pneumatic layer.
Further, a path 5A for introducing compressed air is formed in the pipe block 5, the compressed air taken from a joint 14 is supplied to a space formed between a disc member 31 and the thrust bearing member 37 through the path 5A. By introducing compressed air into the space, the thrust bearing member 37 and the shaft 26 fixed thereto are supported in the thrust direction via the pneumatic layer.
As described above, the shaft 26 is supported in the radial and thrust directions by the compressed air taken in from the joints 12, 14, and 15. In this state, the drive current is flown to the magnet wire 28, so as to rotate the shaft 26.
At this time, a light beam is irradiated to the mirror surface 33A of the polygon mirror 33 which is fixed to the shaft 26, through an opening 3A, so that the light beam can be reflected and scanned in a specified direction corresponding to the revolution of the polygon mirror 33.
In the light deflecting apparatus using the rotary polygon mirror 1 having the construction, the shaft 26 is rotated at the speed of approximately 60,000 to 80,000 [rpm], thus the part of the radial bearing heats by viscous friction of the air in the space 25. At this time, since the polygon mirror 33 is fixed to the shaft 26 via the thrust bearing member 37, the thermal conducting path from the heating element is complicated, as a result, the thermal expansion amount and the thermal expansion directions with respect to the fitting portion of the polygon mirror 33 become non-uniform, thus, there is a problem that the running accuracy of the mirror surface 33A of the polygon mirror 33 deteriorates.
Further, because the polygon mirror 33 is fixed to the shaft 26 via the thrust bearing member 37, the length of the shaft of the rotor becomes long, and the natural frequency could not be made sufficiently high. As a result, there is a problem that a stable revolution cannot be realized.